Is this the most famous film of the 1940s? The only alternative candidates I can think of are Citizen Kane and It's A Wonderful Life, although including 1939 would also give you The Wizard of Oz and Gone With The Wind. I'm tempted also to cite the 1941 Maltese Falcon, but Dad hadn't heard of it when we were discussing movies recently.

That's by the by, though. The movie's terrific. Robert McKee uses it in his screenwriting classes, dissecting its story and character motivations until it's lying in front of him in bloody pieces... yet even after he's done all that to it, the film can still make people cry. It also won Oscars for Best Picture, Best Director and Best Adapted Screenplay. It's pitch-perfect, basically. The damn thing sings. The story's nothing particularly unusual, but it does everything right and the cast are playing it so truthfully that it actually improves the movie to know all of its backstory and revelations beforehand. You can see everything that's going on between Bogart and Bergman to such precision that it hurts, even when they're not saying a word.

I see I've started on the cast. Bogart's the main man, obviously. He's playing his first romantic lead and he's a little bit brilliant. He's nothing like his character in The Maltese Falcon only the year before, creating this old, weary cynic who's at once a heartbroken romantic and yet also sufficiently cold and hard that at the end it's perfectly possible that he might double-cross anyone. Bogart really is as good as you'd think he'd have to be, given his reputation. The only bit of his performance I wasn't sure about was his famous "Here's looking at you, kid", oddly enough, and I understand that was an ad-lib. I love everyone, though. Ingrid Bergman is matching Bogart beat for beat and the two of them have such chemistry that it's surprising they never again worked together, although apparently it was a problem in filming that he was shorter than her by two inches. Claude Rains is the funniest and the source of most of the film's gags. Peter Lorre doesn't get much screen time, but he's a joy to watch in what's perhaps the perfect Lorre role. Sydney Greenstreet is predictably excellent, but less famous but no less wonderful is S.Z. Sakall as Bogart's fat old assistant manager.

The only one who ever gets criticised, albeit only slightly, is Paul Henreid as Victor Laszlo, but I think it's the right choice for him to be a little distant emotionally. He's not a cold man, but he's so noble and important that he's not really in touch with that level of humanity and grubby compromise that's done so much damage to all the other characters. It's possible that this is the actor's own personality showing through, though. Henreid wasn't well-liked on set. He hadn't even wanted to do the film in the first place. Selznick International Pictures lent him to Warners against his will and he thought playing a supporting role would undermine his image as a romantic lead, but they won him around by giving him top billing along with Bogart and Bergman. He thought Bogart a mediocre actor, incidentally, while Bergman thought Henreid a prima donna.

More significant than you'd think is the fact that it's a wartime movie made in wartime. The Allied invasion of Casablanca in November 1942 nearly got studio executives shooting a new ending to reflect current events, for instance. Furthermore the Office of War Information amusingly prevented the film from being shown to the troops in North Africa, for fear of offending Vichy supporters. They would been offended, yes. The film's arguably harsher towards Vichy collaboration than it is towards the Germans. Warner Bros had actually been the first Hollywood studio to oppose Hitler's regime and to refuse to show its films in German-occupied territories, with Harry M. Warner having been making anti-Nazi speeches in Germany as early as 1936.

The key element in this though is that almost all the actors really were from Europe. Conrad Veidt as Major Heinrich Strasser for instance was indeed a German, but so anti-Nazi that his reason for fleeing his homeland had been an SS death squad having been sent to kill him. There are only three American-born actors in the credits: Bogart, Dooley Wilson and Joy Page. There were even lots of Europeans among the minor parts and extras, so there were real tears when they filmed the duel of the national anthems, for instance. Those aren't fake emotions you're seeing.

In other words, the actors are nailing it. As for the script, by all rights it should have been rubbish. It was an adaptation of an unstaged play, it wasn't complete when they started shooting and they had multiple scriptwriters all doing their own versions. The Epstein twins made it funnier, Howard Koch heightened the melodrama and politics, an uncredited Casey Robinson wrote all the Ilsa-Rick meetings in the cafe and the director was apparently most interested in the love story. Then on top of all that you've got the Production Code Administration censoring anything they disapproved of. This should have resulted in a train wreck, yet somehow it worked. Koch thought this was because of the tensions: "Surprisingly, these disparate approaches somehow meshed, and perhaps it was partly this tug of war between Curtiz and me that gave the film a certain balance." It's a love story, but also a wartime drama. It's got a sledgehammer political message, but that's good because what they're saying boils down to "don't collaborate with Nazis". Personally though I think a lot of it's because it has strong, unified themes. You've got sacrifice. You've got the compromises people either make or don't make in the face of evil. You've got political allegory, with characters' choices reflecting the greater ones of their nations. Then you've got the lies.

Wow, those lies. Everyone tells them. Rains's are particularly blatant. Sometimes they're just a flippant way of not answering the question, as with Bogart telling the Germans that his nationality is "drunkard". There are self-serving lies and noble lies, but the latter can tear people apart even if the motives behind them were impeccable. In wartime, the truth is dangerous. Honesty can kill as surely as a bullet, but that doesn't mean that Bogart's Rick isn't a shell of a man because of them. Oh, and that's without getting into the self-sacrifice. When it comes to this particular theme, I can't think of another film that explores it with even half this depth.

The original play was inspired by first-hand experience of the Nazis in Vienna after the Anschluss, incidentally. In terms of plot holes it's bunk, though. Nothing like the all-important letters of transit ever existed. They're a plot device dreamed up by the writers, who were apparently surprised no one ever called them on it. The English subtitles even suggest they'd been signed by De Gaulle, which would have carried as much weight with the Germans as Churchill or Roosevelt. I also don't see why Major Strasser didn't bring some soldiers with him at the finale, while most obviously it makes no sense that Laszlo isn't whisked off to a dungeon the moment anyone sets eyes on him. However the latter's such a brazen plot hole that the film carries it off through sheer effrontery.

However none of that matters. The film's telling the truth about wartime emotions and the dilemmas associated with love, heroism and selfishness. You've got good people doing bad things and corrupt people being extremely funny. Claude Rains is wonderful, but what his character nearly does to that Bulgarian girl... brrr. In 2006 the Writers Guild of America named this the best screenplay ever written, you know. Umberto Eco thinks that "by any strict critical standards" it's mediocre, though.

At the end of the day, this isn't one of those slightly daunting so-called classics that you watch because it's good for you. It's not trying to be high art. No one expected it to be anything special at the time. It's cool, it's entertaining and it can be surprising even when you've seen it before. It's rather extraordinary how much time it spends at the beginning in just setting up its world, for instance, exploring Casablanca and Rick's cafe through all those overlapping vignettes and colourful characters. Furthermore there's nothing pre-ordained about the finale, with Rick in no way faking the fact that he's selling up and selling out. There's no question that he's getting ready to do some double-crossing, except that you can't be sure of whom. Even I don't know when he decided. Maybe he didn't either.

I think the film hit me harder on this watching. I'm always entertained by the Bogart-Rains relationship and the Vichy-bashing, but on a more serious note the Bulgarian girl's vignette is a heartbreaker and I could watch Bogart and Bergman all day. Roger Ebert thinks this is "probably on more lists of the greatest films of all time than any other single title, including Citizen Kane" and I'd guess he's right. Don't set your expectations to Intercontinental Super-Ballistic Greatest Thing Ever, but do expect a damn good film. I'm sure you've already seen it, though. I'm always a little surprised to meet adults who haven't.